Assume you want to use a PIN LOCK on your Microsoft Account; you can do this without routinely using the account password in your windows machine. A PIN can only be used to unlock the device you activate it on.
Thus, if someone steals the PIN you used to unlock your laptop with, they will have access to only that one laptop and not your entire Microsoft account. This PIN should only work to the device you set it up on and not to any other devices.